Method of fabricating a light emitting device

ABSTRACT

There is provided an inexpensive light emitting device and an electronic instrument using the same. In this invention, photolithography steps relating to manufacture of a transistor are reduced, so that the yield of the light emitting device is improved and the manufacturing period thereof is shortened. A feature is that a gate electrode is formed of conductive films of plural layers, and by using the selection ratio of those at the time of etching, the concentration of an impurity region formed in an active layer is adjusted.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a device (hereinafter referredto as a light emitting device) including an element (hereinafterreferred to as a light emitting element) having a luminous materialinterposed between electrodes. Particularly, the present inventionrelates to a light emitting device including a light emitting element(hereinafter referred to as an EL element) using, as a luminousmaterial, an organic compound in which EL (Electro Luminescence) isobtained. Incidentally, an organic EL display and an organic lightemitting diode (OLED: Organic Light Emitting Diode) are included in thelight emitting device of the present invention.

[0003] The luminous material which can be used for the present inventionincludes any luminous materials which emit light (phosphorescence and/orfluorescence) through singlet excitation, triplet excitation, or bothexcitations.

[0004] 2. Description of the Related Art

[0005] In recent years, research of an EL element has proceeded in whicha thin film capable of obtaining EL and made of an organic compound isinterposed between an anode and a cathode, and development of a lightemitting device using self luminescence of the EL element has proceeded.In the development of this light emitting device, although a passivematrix type has been the mainstream, there is a fear that when a pixelportion becomes highly fine, the light emitting brightness of the ELelement must be increased, so that the reliability (the long life of theEL element) can not be secured.

[0006] Then, recently, attention has been paid to an active matrix typein order to attain a highly fine display. The active matrix type lightemitting device has a feature that an input signal is controlled by asemiconductor element provided in each pixel to make an EL element emitlight, and a transistor is generally used as the semiconductor element.

[0007] A typical pixel structure is such that two transistors areincluded in a pixel and have different roles respectively, and the lightemitting brightness of the EL element can be controlled. As a result, alight emitting period is almost equivalent to one frame period, and evenif a pixel portion becomes highly fine, it becomes possible to displayan image while the light emitting brightness is suppressed. Thus, it hasbeen considered that the active matrix type is effective for a lightemitting device including a highly fine pixel portion.

[0008] However, in the active matrix type light emitting device, aplurality of transistors are formed on the same substrate, and it isdifficult to ensure the yield as compared with a passive matrix type ofa simple structure. Besides, since a manufacturing process of atransistor is relatively complicated, there is a fear that themanufacturing cost becomes high as compared with the passive matrix typelight emitting device. Further, in that case, there is a fear that theunit cost of an electric instrument using the active matrix type lightemitting device as its display portion is also raised.

SUMMARY OF THE INVENTION

[0009] The present invention has an object to provide a technique forfabricating an active matrix type light emitting device having a lowmanufacturing cost. This object is especially pursued in the lightemitting device having a number of photolithography steps as comparedwith an active matrix type liquid crystal display device.

[0010] Further, the present invention has another object to decrease themanufacturing cost of an electric instrument using the active matrixtype light emitting device as a display portion.

[0011] According to the present invention, photolithography stepsrelating to manufacture of a transistor are reduced, so that the yieldof a light emitting device is improved, the manufacturing period isshortened, and the manufacturing cost is reduced. The feature is that agate electrode is formed of a plurality of conductive films, and theselection ratio of those at the time of etching is used to make a highlyreliable structure. Incidentally, in the present specification, atransistor includes a MOS transistor and a thin film transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIGS. 1A to 1F are views showing manufacturing steps of ann-channel transistor.

[0013]FIGS. 2A to 2E are views showing manufacturing steps of a lightemitting device.

[0014]FIGS. 3A to 3D are views showing manufacturing steps of the lightemitting device.

[0015]FIGS. 4A and 4B are views showing manufacturing steps of the lightemitting device.

[0016]FIGS. 5A and 5B are views showing an upper structure and a crosssectional structure of a light emitting device.

[0017]FIGS. 6A to 6D are views showing manufacturing steps of a lightemitting device.

[0018]FIGS. 7A to 7C are views showing manufacturing steps of a lightemitting device.

[0019]FIGS. 8A to 8E are views showing manufacturing steps of a lightemitting device.

[0020]FIG. 9 is a view showing a manufacturing step of a light emittingdevice.

[0021]FIG. 10 is a view showing a cross sectional structure of a lightemitting device.

[0022]FIGS. 11A and 11B are views each showing a circuit structure of apixel of a light emitting device.

[0023]FIG. 12 is a view showing a cross sectional structure of a lightemitting device.

[0024]FIG. 13 is a view showing a circuit structure of a pixel of alight emitting device.

[0025]FIG. 14 is a view showing a cross sectional structure of a lightemitting device.

[0026]FIGS. 15A to 15C are views showing manufacturing steps of a lightemitting device.

[0027]FIG. 16 is a view showing a circuit structure of a pixel of alight emitting device.

[0028]FIGS. 17A and 17B are views each showing a structure of a lightemitting device having an external driving circuit.

[0029]FIGS. 18A and 18B are views each showing a structure of a lightemitting device having an external controller.

[0030]FIGS. 19A to 19F are views showing specific examples of electricinstruments.

[0031]FIGS. 20A and 20B are views showing specific examples of electricinstruments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] An example of fabricating steps of an n-channel transistorcharacterizing the present invention will be described with reference toFIGS. 1A to 1F. In FIG. 1A, reference numeral 100 designates aninsulator which is a substrate provided with an insulating film on itssurface, an insulating substrate, or an insulating film. A semiconductorfilm (typically, a silicon film) 101 is formed on the insulator 100, andthis semiconductor film 101 becomes an active layer of a transistor. Thesemiconductor film 101 is covered with an insulating film 102 containingsilicon, and this insulating film 102 becomes a gate insulating film ofthe transistor. As the insulating film containing silicon, it ispossible to use a silicon oxide film, a silicon nitride film, a siliconnitride oxide film, or a laminate film of a combination of these.

[0033] Next, a conductive film in which at least two conductive filmsare laminated, is formed on the insulating film 102 containing silicon.Here, a first conductive film 103 and a second conductive film 104 areformed. Here, it is preferable to make such a combination that theselection ratio at the time of etching can be secured between the firstconductive film 103 and the second conductive film 104.

[0034] As a typical example of such a combination, it is possible toenumerate 1) combination of a tantalum nitride film as the firstconductive film and a tungsten film as the second conductive film, 2)combination of a tungsten film as the first conductive film and analuminum alloy film as the second conductive film, and 3) combination ofa titanium nitride film as the first conductive film and a tungsten filmas the second conductive film.

[0035] In the combination 1), the tungsten film and the tantalum nitridefilm are etched by a combination of chlorine (Cl₂) gas and a carbontetrafluoride (CF₄) gas, and an etching rate of the tantalum nitridefilm is extremely lowered by adding an oxygen (o₂) gas to this gassystem, so that the selection ratio can be secured.

[0036] In the combination 2), although the aluminum film is etched by acombination of a bromine trichloride (BCl₃) gas and a chlorine (Cl₂)gas, the tungsten film is not etched. Besides, although the tungstenfilm is etched by a combination of a chlorine (Cl₂) gas and a carbontetrafluoride (CF₄) gas, the aluminum film is not etched. In this way,the selection ratio of both can be secured.

[0037] In the case where the aluminum alloy film is used as the secondconductive film, it is preferable to provide a titanium film or atitanium nitride film as a third conductive film thereon. By doing so,contact resistance to another wiring line can be lowered, and further,there is also obtained such a merit that hillocks generated in aluminumalloy can be suppressed.

[0038] Next, as shown in FIG. 1B, the second conductive film 104 isetched by using a resist 105, and an electrode 106 made of the secondconductive film is formed. As an etching condition, it is preferable toperform a dry etching using ICP (Inductively Coupled Plasma). As anetching gas, a mixture gas of a carbon tetrafluoride (CF₄) gas, achlorine (Cl₂) gas and an oxygen (O₂) gas is used.

[0039] As a typical etching condition, a gas pressure is made 1 Pa, andin this state, RF electric power (13.56 MHz) of 500 W is applied to acoil type electrode to produce plasma. Besides, RF electric power (13.56MHz) of 150 W is applied as a self bias voltage to a stage on which thesubstrate is put, so that a negative self bias is applied to thesubstrate. At this time, it is appropriate that the amount of the flowof the respective gases is made such that the carbon tetrafluoride gashas a flow of 2.5×10⁻⁵ m³/min, the chlorine gas has a flow of 2.5×10⁻⁵m³/min, and the oxygen gas has a flow of 1.0×10⁻⁵ m³/min. The etchingrate of the tantalum nitride film is suppressed by the existence ofoxygen.

[0040] In this state, an impurity element (hereinafter referred to as ann-type impurity element) for making a semiconductor an n-typesemiconductor is added to the semiconductor film 101. At this time,since the gate insulating film 102 is covered with the first conductivefilm 103, the electrode 106 made of the second conductive film is usedas a mask, and the n-type impurity element is made to pass through thefirst conductive film 103 and is added. That is, the n-type impurityelement is added to the semiconductor film 101 by self-alignment usingthe electrode 106 made of the second conductive film. Specifically, anelement (typically, phosphorus or arsenic) belonging to group 15 of theperiodic table can be used as the n-type impurity element.

[0041] At this time, a well-known plasma doping method or ionimplantation method may be used as an adding method. The concentrationof the element added in the semiconductor film may be made 1×10²⁰ to1×10²¹ atoms/cm³. Regions 107 and 108 in which the n-type impurityelement of the concentration like this is added are called n-typeimpurity regions (a) in the present specification.

[0042] Next, as shown in FIG. 1C, the first conductive film 103 isetched by self-alignment using the electrode 106 made of the secondconductive film as a mask. By this, an electrode 109 made of the firstconductive film is formed under the electrode 106 made of the secondconductive film.

[0043] This etching is performed by a dry etching method using the ICP,and a mixture gas of a carbon tetrafluoride (CF₄) gas and a chlorine(Cl₂) gas is used as an etching gas. A typical etching condition is suchthat a gas pressure is made 1 Pa, and RF electric power (13.56 MHz) of500 W is applied to a coil type electrode to produce plasma in thisstate. Besides, RF electric power (13.56 MHz) of 20 W is applied as aself bias voltage to the stage on which the substrate is put, so that anegative self bias is applied to the substrate. At this time, it isappropriate that the flow of the respective gases is made such that thecarbon tetrafluoride gas has a flow of 3.0×10⁻⁵ m³/min, and the chlorinegas has a flow of 3.0×10⁻⁵ m³/min.

[0044] Next, as shown in FIG. 1D, the line width of the electrode 106made of the second conductive film is narrowed by etching, and a secondgate electrode 110 is formed. The second gate electrode 110 indicates anelectrode made of the second conductive film and functioning as the gateelectrode of a transistor.

[0045] This etching is performed by a dry etching method using the ICP,and a mixture gas of a carbon tetrafluoride (CF₄) gas, a chlorine (Cl₂)gas and an oxygen (O₂) gas is used as an etching gas. A typical etchingcondition is such that a gas pressure is made 1 Pa, and in this state,RF electric power (13.56 MHz) of 500 W is applied to a coil typeelectrode to produce plasma. Besides, RF electric power (13.56 MHz) of20 W is applied as a self bias voltage to the stage on which thesubstrate is put, so that a negative self bias is applied to thesubstrate. At this time, it is appropriate that the amount of the flowof the respective gases is made such that the carbon tetrafluoride gashas a flow of 2.5×10⁻⁵ m³/min, the chlorine gas has a flow of 2.5×10⁻⁵m³/min, and the oxygen gas has a flow of 1.0×10⁻⁵ m³/min. The etchingrate of the tantalum nitride film is suppressed by the existence ofoxygen.

[0046] Next, an adding step of the n-type impurity element is againcarried out. At this time, in regions designated by reference numerals111 and 112, regions are formed in which the n-type impurity elementhaving a concentration of 1×10¹⁷ to 1×10¹⁹ atoms/cm³ is added. Theregions 111 and 112 in which the n-type impurity element of theconcentration like this is added, are called n-type impurity regions (b)in the present specification.

[0047] In this adding step, a portion where the conductive films of atleast two layers are laminated, that is, a laminate portion of theelectrode 109 made of the first conductive film and the second gateelectrode 110 becomes a mask, and the n-type impurity element is made topass through a portion where only the electrode 109 made of the firstconductive film is exposed and is added. That is, the n-type impurityelement is added to the semiconductor film 101 by self-alignment usingthe second gate electrode 110.

[0048] A region 113 where the n-type impurity element is not added is aregion functioning as a channel formation region of the transistor, andis formed just under the second gate electrode 110.

[0049] Next, as shown in FIG. 1E, the line width of the electrode 109made of the first conductive film is narrowed by etching, and a firstgate electrode 114 is formed. Note that, the first gate electrode 114indicates an electrode made of the first conductive film and functioningas the gate electrode of a transistor.

[0050] This etching is performed by a dry etching method using the ICPor a dry etching method with an RIE (Reactive Ion Etching) mode, and amixture gas of a carbon tetrafluoride (CF₄) gas and a chlorine (Cl₂) gasis used as an etching gas. A typical etching condition is such that agas pressure is made 1 Pa, and RF electric power (13.56 MHz) of 500 W isapplied to a coil type electrode to produce plasma in this state.Besides, RF electric power (13.56 MHz) of 20 W is applied as a self biasvoltage to the stage on which the substrate is put, so that a negativeself bias is applied to the substrate. At this time, it is appropriatethat the amount of the flow of the respective gases is made such thatthe carbon tetrafluoride gas has a flow of 2.5×10⁻⁵ m³/min, the chlorinegas has a flow of 2.5×10⁻⁵ m³/min, and the oxygen gas has a flow of1.0×10⁻⁵ m³/min.

[0051] Note that, although this etching step has an object to etch theelectrode 109 made of the first conductive film (tantalum nitride film),the etching rate of the tantalum nitride film is suppressed by addingthe oxygen gas. This is for achieving fine adjustment of the etchingamount of the electrode 109 made of the first conductive film.

[0052] At this time, a feature is that etching is stopped at a placewhere an end portion of the first gate electrode 114 overlaps a part ofeach of the n-type impurity regions (b) 111 and 112 through the gateinsulating film 102. That is, the n-type impurity region (b) 111 isdivided into a region 11 a not overlapping the first gate electrode 114and a region 111 b overlapping there through the gate insulating film102. The n-type impurity region (b) 112 is also divided into a region112 a not overlapping the first gate electrode 114 and a region 112 boverlapping there through the gate insulating film 102.

[0053] Thereafter, as shown in FIG. 1F, when a passivation film 116, aninterlayer insulating film 117, a source wiring line 118 being incontact with the semiconductor film which becomes the active layer ofthe transistor, and a drain wiring line 119 are formed, the n-channeltransistor is completed. As the passivation film 116, a silicon nitridefilm or a silicon nitride oxide film may be used. As the interlayerinsulating film 117, an inorganic insulating film, an organic insulatingfilm, or a laminate film of those may be used. As the organic insulatingfilm, a resin film of polyimide, acryl resin, polyamide, or BCB(benzocyclobutene) may be used. Besides, a well-known conductive filmmay be used as the source wiring line 118 and the drain wiring line 119.

[0054] In the above fabricating steps, photolithography steps arecarried out for four times, that is, at the time of formation of thesemiconductor film 101, at the time of formation of the electrode 106made of the second conductive film, at the time of formation of contactholes of the interlayer insulating film 117, and at the time offormation of the source wiring line 118 and the drain wiring line 119.In the case where a CMOS circuit is formed, although thephotolithography steps are increased by one in order to fabricate ap-channel transistor, the steps are carried out only for five timesnevertheless.

[0055] In the transistor of FIG. 1F, the n-type impurity region (b) 112is formed between the channel formation region 113 and the drain region108. Here, in the n-type impurity region (b) 112, the region designatedby reference numeral 112 b overlaps the first gate electrode 114 throughthe gate insulating film 102, and this structure is very effective toprevent hot carrier deterioration. Besides, in the n-type impurityregion (b) 112, the region designated by the reference numeral 112 a isa region having the same function as a conventional LDD (Lightly DopedDrain) region.

[0056] Accordingly, in the transistor of FIG. 1F, a hot carriercountermeasure is taken by the region 111 b or 112 b, and a leak currentcountermeasure is taken by the region 111 a or 112 a, so that a highlyreliable structure is made. Like this, since the highly reliabletransistor can be fabricated through the five photolithography steps,not only the improvement of the yield of the light emitting deviceincluding the light emitting element and the shortening of themanufacturing period are realized, but also the inexpensive and highlyreliable light emitting device can be fabricated.

[0057] Hereinafter, embodiment mode of the present invention will bedescribed in detail using the embodiments described below.

[0058] (Embodiment 1)

[0059] In this embodiment, a description will be given of a method ofmanufacturing a pixel portion and a driving circuit provided at itsperiphery on the same insulator. However, for simplification of thedescription, with respect to the driving circuit, a CMOS circuit inwhich an n-channel transistor and a p-channel transistor are combinedwill be shown.

[0060] First, as shown in FIG. 2A, a glass substrate 201 is prepared. Inthis embodiment, not-shown protection films (carbon films, specificallydiamond-like carbon films) are provided on both surfaces (the frontsurface and the rear surface) of the glass substrate 201. As long as itis transparent to visible light, a material other than glass (forexample, plastic) may be used.

[0061] Next, an under film 202 having a thickness of 300 nm is formed onthe glass substrate 201. In this embodiment, as the under film 202,silicon nitride oxide films are laminated and are used. At this time, itis appropriate that the concentration of nitrogen of a layer adjacent tothe glass substrate 201 is made 10 to 25 wt %, and nitrogen is made tobe contained at the concentration rather higher than that of anotherlayer.

[0062] Next, an amorphous silicon film (not shown) having a thickness of50 nm is formed on the under film 202 by a sputtering method. Note that,it is not necessary to limit the film to the amorphous silicon film, butany semiconductor films (including a microcrystalline semiconductorfilm) containing amorphous structure may be used. As the amorphoussemiconductor film, an amorphous silicon film or an amorphous silicongermanium film (a silicon film containing germanium at a concentrationof 1×10¹⁸ to 1×10²¹ atoms/cm³) may be used. The film thickness may be 20to 100 nm.

[0063] Then, crystallization of the amorphous silicon film is performedby using a well-known laser crystallizing method, and a crystallinesilicon film 203 is formed. In this embodiment, although a solid laser(specifically, second harmonic of Nd:YAG laser) is used, an excimerlaser may also be used. As the crystallizing method, a furnace annealingmethod may be used.

[0064] Next, as shown in FIG. 2B, the crystalline silicon film 203 isetched by a first photolithography step to form island-like crystallinesilicon films 204 to 207. These are crystalline silicon films whichsubsequently become the active layers of transistors.

[0065] Note that, in this embodiment, although the crystalline siliconfilms are used as the active layers of the transistors, an amorphoussilicon film can also be used as the active layer.

[0066] Here, in this embodiment, a protection film (not shown) made of asilicon oxide film and having a thickness of 130 nm is formed on theisland-like crystalline silicon films 204 to 207 by a sputtering method,and an impurity element (hereinafter referred to as a p-type impurityelement) to make a semiconductor a p-type semiconductor is added to theisland-like crystalline silicon films 204 to 207. As the p-type impurityelement, an element (typically, boron or gallium) belonging to group 13of the periodic table can be used. Note that, this protection film isprovided to prevent the crystalline silicon film from directly beingexposed to plasma when the impurity is added, and to enable fineconcentration control.

[0067] The concentration of the p-type impurity element added at thistime may be made 1×10¹⁵ to 5×10¹⁷ atoms/cm³ (typically, 1×10¹⁶ to 1×10¹⁷atoms/cm³). The p-type impurity element added at this concentration isused to adjust the threshold voltage of the n-channel transistor.

[0068] Next, the surfaces of the island-like crystalline silicon films204 to 207 are washed. First, the surface is washed by using pure watercontaining ozone. At that time, since a thin oxide film is formed on thesurface, the thin oxide film is removed by using a hydrofluoric acidsolution diluted to 1%. By this treatment, contaminants adhered to thesurfaces of the island-like crystalline silicon films 204 to 207 can beremoved. At this time, it is preferable that the concentration of ozoneis 6 mg/L or more. The series of treatments are carried out withoutopening to the air.

[0069] Then, a gate insulating film 208 is formed to cover theisland-like crystalline silicon films 204 to 207. As the gate insulatingfilm 208, an insulating film having a thickness of 10 to 150 nm,preferably 50 to 100 nm and containing silicon may be used. This mayhave a single-layer structure or a laminate structure. In thisembodiment, a silicon nitride oxide film having a thickness of 80 nm isused.

[0070] In this embodiment, the steps from the surface washing of theisland-like crystalline silicon films 204 to 207 to the formation of thegate insulating film 208 are carried out without opening to the air, sothat contaminants and interface levels on the interface between thesemiconductor film and the gate insulating film are lowered. In thiscase, a device of a multi-chamber system (or an inline system) includingat least a washing chamber and a sputtering chamber may be used.

[0071] Next, a tantalum nitride film having a thickness of 30 nm isformed as a first conductive film 209, and further, a tungsten filmhaving a thickness of 370 nm is formed as a second conductive film 210.In addition, a combination of a tungsten film as the first conductivefilm and an aluminum alloy film as the second conductive film, or acombination of a titanium film as the first conductive film and atungsten film as the second conductive film may be used.

[0072] These metal films may be formed by a sputtering method. When aninert gas such as Xe or Ne is added as a sputtering gas, film peelingdue to stress can be prevented. When the purity of a tungsten target ismade 99.9999%, a low resistance tungsten film having a resistivity of 20mωcm or less can be formed.

[0073] Besides, the steps from the surface washing of the semiconductors204 to 207 to the formation of the second conductive film 210 can alsobe carried out without opening to the air. In this case, a device of amulti-chamber system (or an inline system) including at least a washingchamber, a sputtering chamber for forming an insulating film, and asputtering chamber for forming a conductive film may be used.

[0074] Next, resists 211 a to 211 e are formed, and the secondconductive film 210 is etched. As an etching condition here, thecondition explained in FIG. 1B may be adopted (FIG. 2C).

[0075] By this, the second conductive film (tungsten film) 210 isselectively etched, and electrodes 212 to 216 made of the firstconductive film are formed. The reason why the second conductive film210 is selectively etched is that the progress of etching of the firstconductive film (tantalum nitride film) becomes extremely slow byaddition of oxygen to the etching gas.

[0076] Note that, here, there is a reason why the first conductive film209 is made to remain. Although the first conductive film can also beetched at this time, if the first conductive film is etched, the gateinsulating film 208 is also etched in the same step and the filmthickness is decreased. At this time, if the thickness of the gateinsulating film 208 is 100 nm or more, there is no problem. However, ifthe thickness is less than that, a part of the gate insulating film 208is removed in a subsequent step and the semiconductor film thereunder isexposed, and there is a possibility that the semiconductor film whichbecomes a source region or a drain region of a transistor is alsoremoved.

[0077] However, the foregoing problem can be solved by leaving the firstconductive film 209 as in this embodiment.

[0078] Next, an n-type impurity element (in this embodiment, phosphorus)is added in a self-aligning manner by using the resists 211 a to 211 eand the electrodes 212 to 216. At this time, phosphorus passes throughthe first conductive film 209 and is added. Impurity regions 217 to 225formed in this way contain the n-type impurity element at aconcentration of 1×10²⁰ to 1×10²¹ atoms/cm³ (typically, 2×10²⁰ to 5×10²¹atoms/cm³).

[0079] Next, the first conductive film 209 is etched by using theresists 211 a to 211 e as masks. As an etching condition here, thecondition explained in FIG. 1C may be adopted. In this way, electrodes226 to 230 made of the first conductive film are formed (FIG. 2D).

[0080] Next, as shown in FIG. 2E, the electrodes 212 to 216 made of thesecond conductive film are selectively etched by using the resists 211 ato 211 e as they are. As an etching condition here, the conditionexplained in FIG. 1D may be adopted. In this way, second gate electrodes231 to 235 are formed.

[0081] Next, an n-type impurity element (in this embodiment, phosphorus)is added. In this step, the second gate electrodes 231 to 235 functionas masks, and phosphorus passes through part of the electrodes 226 to230 made of the first conductive film and is added, and n-type impurityregions 236 to 245 containing phosphorus at a concentration of 2×10¹⁶ to5×10¹⁹ atoms/cm³ (typically, 5×10¹⁷ to 5×10¹⁸ atoms/cm³) are formed.

[0082] Besides, as an addition condition here, an acceleration voltageis set quite high as 70 to 120 kV (in this embodiment, 90 kV) so thatphosphorus passes through the first conductive film and the gateinsulating film and reaches the island-like crystalline silicon films.

[0083] Next, as shown in FIG. 3A, the electrodes 226 to 230 made of thefirst conductive film are etched to form first gate electrodes 246 to250. As an etching condition here, the condition explained in FIG. 1Emay be adopted.

[0084] At this time, the first gate electrodes 246 to 250 are etched sothat they partially overlap the n-type impurity regions (b) 236 to 245through the gate insulating film 208. For example, the n-type impurityregion (b) 236 is divided into a region 236 a not overlapping the firstgate electrode 246 and a region 236 b overlapping there through the gateinsulating film 208. The n-type impurity region (b) 237 is divided intoa region 237 a not overlapping the first gate electrode 246 and a region237 b overlapping there through the gate insulating film 208.

[0085] Next, resists 251 a and 251 b are formed, and an impurity element(hereinafter referred to as a p-type impurity element) to make asemiconductor a p-type semiconductor is added. As the p-type impurityelement, an element (typically, boron) belonging to group 13 of theperiodic table may be added. Here, an acceleration voltage is set sothat boron passes through the first gate electrodes 247 and 250 and thegate insulating film 208, and reaches the semiconductor film. In thisway, p-type impurity regions 252 to 255 are formed (FIG. 3B).

[0086] Next, as shown in FIG. 3C, as a first inorganic insulating film256, a silicon nitride film or silicon nitride oxide film having athickness of 30 to 100 nm is formed. Thereafter, the added n-typeimpurity element and p-type impurity element are activated. As anactivation means, a furnace annealing, a laser annealing, a lampannealing, or a combination of those can be used.

[0087] Next, as shown in FIG. 3D, a second inorganic insulating film 257made of a silicon nitride film or a silicon nitride oxide film is formedto a thickness of 50 to 200 nm. After the second inorganic insulatingfilm 257 is formed, a heat treatment in the temperature range of 350 to450° C. is carried out. Note that, it is effective to carry out a plasmatreatment using a hydrogen (H₂) gas or an ammonia (NH₃) gas before thesecond inorganic insulating film 257 is formed.

[0088] Next, as an organic insulating film 258, a resin film transparentto visible light is formed to a thickness of 1 to 2 μm. As the resinfilm, a polyimide film, a polyamide film, an acryl resin film, or a BCB(benzocyclobutene) film may be used. Besides, a photosensitive resinfilm can also be used.

[0089] Note that, in this embodiment, the laminate film of the firstinorganic insulating film 256, the second inorganic insulating film 257,and the organic insulating film 258 is generically called an interlayerinsulating film.

[0090] Next, as shown in FIG. 4A, a pixel electrode (anode) 259 made ofan oxide conductive film which has a large work function and istransparent to visible light is formed to a thickness of 80 to 120 nm onthe organic insulating film 258. In this embodiment, an oxide conductivefilm in which gallium oxide is added to zinc oxide is formed. Besides,as another oxide conductive film, it is also possible to use an oxideconductive film made of indium oxide, zinc oxide, tin oxide, or acompound of combination of those.

[0091] Note that, after the oxide conductive film is formed, althoughpatterning is carried out to form the pixel electrode 259, a flatteningtreatment of the surface of the oxide conductive film can also becarried out before the patterning. The flattening treatment may be aplasma treatment or a CMP (Chemical Mechanical Polishing) treatment.Besides, flattening can also be made by using a treatment of rubbingwith a high molecular material (for example, polyvinyl alcohol polymer)or the like.

[0092] Next, contact holes are formed in the interlayer insulating film,and wiring lines 260 to 266 are formed. At this time, the wiring line266 is formed to be connected with the pixel electrode 259. In thisembodiment, this wiring line is made as the laminate film of three-layerstructure in which a titanium film having a thickness of 150 nm, analuminum film containing titanium and having a thickness of 300 nm, anda titanium film having a thickness of 100 nm are continuously formedfrom the lower layer side by a sputtering method.

[0093] At this time, the wiring lines 260 and 262 function as sourcewiring lines of a CMOS circuit, and the wiring line 261 functions as adrain wiring line. The wiring line 263 is a source wiring line of aswitching transistor, and the wiring line 264 is a drain wiring line ofthe switching transistor. The wiring line 265 is a source wiring line(equivalent to a current supply line) of a current control transistor,and the wiring line 266 is a drain wiring line of the current controltransistor and is connected with the pixel electrode 259.

[0094] Next, as shown in FIG. 4B, an insulating film (hereinafterreferred to as a bank) 267 having an opening portion on the pixelelectrode is formed. The bank 267 may be formed by patterning aninsulating film having a thickness of 100 to 400 nm and containingsilicon or an organic resin film. This bank 267 is formed to fill aportion between a pixel and a pixel (between a pixel electrode and apixel electrode). Besides, it also has an object to prevent asubsequently formed organic EL film such as a light emitting layer frombeing brought into direct contact with the end portion of the pixelelectrode 259.

[0095] Incidentally, since the bank 267 is an insulating film, attentionmust be paid to electrostatic damage of a device at the time of filmformation. When carbon particles or metal particles are added into theinsulating film, which becomes a material of the bank, to lower itsresistivity, the generation of static electricity at the time of filmformation can be suppressed. In that case, it is appropriate that theamount of addition of carbon particles or metal particles is adjusted sothat the resistivity of the insulating film, which becomes a material ofthe bank 267, becomes 1×10⁶ to 1×10¹² Ωm (preferably, 1×10⁸ to 1×10¹⁰Ωm).

[0096] When the carbon particles or the metal particles are added to thebank 267, optical absorption is raised and transmissivity is lowered.That is, since light from the outside of the light emitting device isabsorbed, it is possible to avoid such a disadvantage that an outsidescene is reflected in the cathode surface of the EL element.

[0097] Next, an EL layer 268 is formed by an evaporation method.Incidentally, in this embodiment, a laminate layer of a hole injectinglayer and a light emitting layer is called an EL layer. That is, alaminate layer of a combination of a hole injecting layer, a holetransporting layer, a hole blocking layer, an electron transportinglayer, an electron injecting layer, or an electron blocking layer and alight emitting layer is defined as the EL layer. In this embodiment, itis possible to use a well-known light emitting layer, hole injectinglayer, hole transporting layer, hole blocking layer, electrontransporting layer, electron injecting layer, or electron blockinglayer.

[0098] In this embodiment, first, as the hole injecting layer, a copperphthalocyanine (CuPc) film is formed to a thickness of 20 nm, andfurther, aluminum quinolinolato complex (Alq₃) is formed to a thicknessof 80 nm as the light emitting layer. Besides, a dopant (typically,fluorescent pigment) which becomes a light emitting center may be addedto the light emitting layer by codeposition.

[0099] Next, after the EL layer 268 is formed, a cathode 269 made of aconductive film which has a small work function is formed to a thicknessof 300 nm. As the conductive film having the small work function, aconductive film containing an element belonging to group 1 or group 2 ofthe periodic table may be used. In this embodiment, a conductive filmmade of a compound of lithium and aluminum is used.

[0100] In this way, an EL element 270 including the pixel electrode(anode) 259, the EL layer 268, and the cathode 269 is formed.

[0101] Note that, it is effective to provide a passivation film 271 tocompletely cover the EL element 270 after the cathode 269 is formed. Asthe passivation film 271, a single layer of an insulating film includinga carbon film, a silicon nitride film, or a silicon nitride oxide film,or a laminate layer of a combination of the insulating films is used.

[0102] At this time, it is preferable to use a film having an excellentcoverage as the passivation film, and it is effective to use a carbonfilm, especially a DLC (Diamond-Like Carbon) film. Since the DLC filmcan be formed in the temperature range of from room temperature to 100 Cor less, it can also be formed easily over the EL layer 268 having lowheat resistance. Besides, the DLC film has a high blocking effect tooxygen, and can suppress oxidation of the EL layer 268. Thus, it ispossible to prevent such a problem that the EL layer 268 is oxidizedduring a subsequently performed sealing step.

[0103] Further, a seal member (not shown) is provided on the substrate201 (or the under film 202) so as to surround at least the pixelportion, and a cover member 272 is bonded. As the seal member 569, anultraviolet ray curing resin which has little degassing and resistanceto the permeation of water and oxygen may be used. A space 273 may befilled with an inert gas (nitrogen gas or rare gas), a resin(ultraviolet ray curing resin or epoxy resin) or an inert liquid.

[0104] Besides, it is effective to provide a material having a moistureabsorption effect or a material having an oxidation preventing effect inthe space 273. As the cover member 272, a glass substrate, a metalsubstrate (preferably a stainless substrate), a ceramic substrate or aplastic substrate (including a plastic film) may be used. In the casewhere the plastic substrate is used, it is preferable to provide acarbon film (preferably a diamond-like carbon film) on the front surfaceand the rear surface to prevent the permeation of oxygen and water.

[0105] In this way, the light emitting device as shown in FIG. 4B iscompleted. Note that, it is effective that after the bank 267 is formed,the steps up to the formation of the passivation film 271 arecontinuously performed by using a film formation device of amulti-chamber system (or an inline system) without opening to the air.By further developing it, it is also possible to continuously performthe steps up to the bonding of the cover member 272 without opening tothe air.

[0106] In this way, an n-channel transistor 601, a p-channel transistor602, a switching transistor (a transistor functioning as a switchingelement for transmitting an image data signal into a pixel) 603, and acurrent control transistor (a transistor functioning as a currentcontrol element for controlling electric current flowing to the ELelement) 604 are formed on the glass substrate 201.

[0107] At this time, the driving circuit includes, as a basic circuit,the CMOS circuit in which the n-channel transistor 601 and the p-channeltransistor 602 are complementarily combined. The pixel portion is formedof a plurality of pixels including the switching transistor 603 and thecurrent control transistor 604.

[0108] The numbers of photolithography steps needed in the manufacturingsteps up to this point is seven times, and they are smaller than that ofa general active matrix type light emitting device. That is, themanufacturing steps of a transistor are greatly simplified, and theimprovement of yield and the reduction of manufacturing cost can berealized.

[0109] Further, as described by the use of FIG. 3A, by providing theimpurity region overlapping the first gate electrode through the gateinsulating film, it is possible to form the n-channel transistor havinghigh resistance to deterioration due to the hot carrier effect. Thus,the light emitting device having high reliability can be realized.

[0110] Further, the light emitting device of the embodiment after theseal (or encapsulation) step for protecting the EL element is performedwill be described with reference to FIGS. 5A and 5B. Note that,reference numerals used in FIGS. 2 to 4 are cited as needed.

[0111]FIG. 5A is a top view showing a state where steps up to sealing ofan EL element are performed, and FIG. 5B is a cross sectional view ofFIG. 5A taken along with the line A-A′. Reference numeral 501 of aportion shown by a dotted line designates a pixel portion; 502, a sourceside driving circuit; and 503, a gate side driving circuit. Referencenumeral 504 designates a cover member; 505, a first seal member; and506, a second seal member.

[0112] Note that, reference numeral 507 designates a wiring line fortransmitting signals inputted to the source side driving circuit 502 andthe gate side driving circuit 503, which receives a video signal and aclock signal from an FPC (Flexible Print Circuit) 508 as an externalinput terminal. Note that, although only the FPC is shown here, a printwiring board (PWB) may be attached to the FPC.

[0113] Next, a cross sectional structure will be described withreference to FIG. 5B. A pixel portion 501 and a source side drivingcircuit 502 are formed on a glass substrate 201, and the pixel portion501 is formed of a plurality of pixels including a current controllingtransistor 604 and a pixel electrode 259 electrically connected to itsdrain. The source side driving circuit 502 is formed by using a CMOScircuit (see FIG. 4B) in which an n-channel transistor 601 and ap-channel transistor 602 are combined. Note that, a polarizing plate(typically, a circular polarizing plate) may be bonded to the glasssubstrate 201.

[0114] The pixel electrode 259 functions as an anode of the EL element.Banks 267 are formed at both ends of the pixel electrode 259, and an ELlayer 268 and a cathode 269 of the EL element are formed on the pixelelectrode 259. The cathode 269 functions also as a wiring line common toall pixels, and is electrically connected to the FPC 508 through theconnection wiring line 507. Further, all elements included in the pixelportion 501 and the source side driving circuit 502 are covered with apassivation film 271.

[0115] A cover member 504 is bonded with a first seal member 505. Aspacer may be provided to secure an interval between the cover member504 and the EL element. A space 273 is formed inside of the first sealmember 505. It is desirable that the first seal member 505 is a materialwhich water or oxygen does not permeate. Further, it is effective toprovide a material having a moisture absorption effect or a materialhaving an oxidation preventing effect in the inside of the space 273.

[0116] Note that, it is appropriate that carbon films (specifically,diamond-like carbon films) 509 a and 509 b as protection films areformed to a thickness of 2 to 30 nm on the front surface and the rearsurface of the cover member 504. The carbon film like this has a role toprevent the infiltration of oxygen and water and to mechanically protectthe surface of the cover member 504.

[0117] Besides, after the cover member 504 is adhered, a second sealmember 506 is provided so as to cover the exposed surface of the firstseal member 505. The second seal member 506 can be made of the samematerial as the first seal member 505.

[0118] By encapsulating the EL element in the structure as describedabove, the EL element can be completely cut off from the outside, and itis possible to prevent a material accelerating deterioration due tooxidation of the EL layer such as moisture or oxygen, from infiltratingfrom the outside. Accordingly, the light emitting device having highreliability can be obtained.

[0119] Note that, as shown in FIGS. 5A and SB, the light emitting devicein which the pixel portion and the driving circuit are provided on thesame substrate and the FPC is attached, is especially called a drivingcircuit built-in light emitting device in the present specification.

[0120] The light emitting device fabricated by carrying out thisembodiment can be operated by both a digital signal and an analogsignal.

[0121] (Embodiment 2)

[0122] In this embodiment, an example in which an active matrix typelight emitting device is fabricated by a fabricating process differentfrom the embodiment 1 will be described. FIGS. 6A to 6D are used for thedescription.

[0123] First, in accordance with the fabricating process of theembodiment 1, steps up to FIG. 2C are performed. The state is shown inFIG. 6A. In this embodiment, a selection ratio of a first conductivefilm 209 and a second conductive film 210 is made smaller than theembodiment 1, and the second conductive film 210 is etched. In thiscase, in the etching step of FIG. 2C, it is appropriate that the flow ofan oxygen gas is made 5.0×10⁻⁶ to 8.0×10⁻⁶ m³/min.

[0124] By doing so, in the first conductive film 209, portions which arenot concealed by electrodes 212 to 216 made of the second conductivefilm are slightly etched and the film thickness is decreased. In thisembodiment, an n-type impurity element (in this embodiment, phosphorus)is added in this state, and n-type impurity regions (a) 217 to 225 areformed. An addition condition may follow the step of FIG. 2C.

[0125] Next, in accordance with the etching condition of FIG. 2E of theembodiment 1, the electrodes 212 to 216 made of the second conductivefilm are etched, and second gate electrodes 601 to 605 are formed. Atthis step, in the first conductive film 209, the portions in which thefilm thickness has been decreased at the step of FIG. 6A are removed anddisappeared, and electrodes 606 to 610 made of the first conductive filmremain (FIG. 6B).

[0126] Next, in this state, the n-type impurity element is again addedunder the same condition as FIG. 2E, and n-type impurity regions (b) 611to 620 are formed (FIG. 6C).

[0127] Next, under the same etching condition as FIG. 3A, the electrodes606 to 610 made of the first conductive film are etched, and first gateelectrodes 621 to 625 are formed. At this time, the n-type impurityregion (b) 611 is divided into a region 611 a not overlapping the firstgate electrode 621 and a region 611 b overlapping there through the gateinsulating film. The n-type impurity region (b) 612 is divided into aregion 612 a not overlapping the first gate electrode 621 and a region612 b overlapping there through the gate insulating film (FIG. 6D).

[0128] When subsequent steps are performed in accordance with the stepssubsequent to FIG. 3B, the active matrix type light emitting deviceshown in FIG. 4B is completed. According to this embodiment, since thedecrease of the film thickness of the gate insulating film can besuppressed, it is effective in the case where the thickness of the gateinsulating film becomes as thin as 50 to 100 nm. Note that, thisembodiment is such that the part of the fabricating steps of theembodiment 1 is changed, and the structure of the embodiment 1 can becited for the structure other than the one described in this embodiment.

[0129] (Embodiment 3)

[0130] In this embodiment, an example in which an active matrix typelight emitting device is fabricated by a fabricating process differentfrom the embodiment 1 will be described. FIGS. 7A to 7C are used for thedescription.

[0131] First, in accordance with the fabricating steps of the embodiment1, steps up to FIG. 2C are performed. The state is shown in FIG. 7A.Next, in accordance with the etching condition of FIG. 2E of theembodiment 1, electrodes 212 to 216 made of a second conductive film areetched, and second gate electrodes 701 to 705 are formed (FIG. 7B).

[0132] Next, in this state, an n-type impurity element is again addedunder the same condition as FIG. 2E, and n-type impurity regions (b) 706to 715 are formed.

[0133] Next, under the same etching condition as FIG. 3A, the firstconductive film 209 is etched, and first gate electrodes 716 to 720 areformed. At this time, the n-type impurity region (b) 706 is divided intoa region 706 a not overlapping the first gate electrode 716 and a region706 b overlapping there through the gate insulating film. The n-typeimpurity region (b) 707 is divided into a region 707 a not overlappingthe first gate electrode 716 and a region 707 b overlapping therethrough the gate insulating film (FIG. 7C).

[0134] When subsequent steps are performed in accordance with the stepssubsequent to FIG. 3B, the active matrix type light emitting deviceshown in FIG. 4B is completed. According to this embodiment, since thedecrease of the film thickness of the gate insulating film can besuppressed to the utmost, it is effective in the case where thethickness of the gate insulating film becomes as thin as 50 to 100 nm.Note that, this embodiment is such that the part of the fabricatingsteps of the embodiment 1 is changed, and the structure of theembodiment 1 can be cited for the structure other than the one describedin this embodiment.

[0135] (Embodiment 4)

[0136] In this embodiment, an example of a manufacturing method of acrystalline semiconductor film different to that in Embodiment 1 isdescribed. FIGS. 8 and 9 are referred to in the description.

[0137] First, a glass substrate 801 is prepared, and a first siliconnitride oxide film 802 a with a thickness of 100 nm, a second siliconnitride oxide film 802 b with a thickness of 200 nm, and an amorphoussilicon film 803 with a thickness of 50 nm are formed thereon. At thistime, it is preferable that the concentration of nitrogen contained inthe first silicon nitride film 802 a is made higher than theconcentration of nitrogen contained in the second silicon nitride film802 b (FIG. 8A).

[0138] Next, nickel (Ni) is added by plasma processing to the amorphoussilicon film 803. In the method of adding the nickel, a nickel electrodeis used to form plasma of nitrogen gas, ammonia gas, hydrogen gas ornoble gas. Note that, in place of nickel, palladium, cobalt, platinum,copper, iridium, Or germanium may be used. In this way an amorphoussilicon film 804 added with nickel is obtained (FIG. 8B).

[0139] Next, as a protecting film 805, a silicon oxide film with athickness of 50 to 150 nm is formed. Thereafter, dehydrogenation isconducted in the amorphous silicon film 804 by furnace annealing at 400to 500° C., and then crystallization of the amorphous silicon film 804by furnace annealing at 550 to 650° C. is performed. With thiscrystallization process, the crystalline silicon film 806 is formed(FIG. 8C).

[0140] Note that, in this embodiment, the series of processes of formingthe first silicon nitride film 802 a, forming the second silicon nitridefilm 802 b, forming the amorphous silicon film 803, plasma processing ofnickel, and forming of the protecting film 805 are continuouslyperformed in the same device. For the processes, a device with a multichamber method having the respective film formation chambers and aplasma processing chamber (a cluster tool method) may be used.

[0141] Next, a p-type impurity element (in this embodiment, boron) maybe added into the crystalline silicon film 806 from above the protectingfilm 805. The concentration of boron added at this time may be 1×10¹⁵ to1×10¹⁸ atoms/cm³. In this way a crystalline silicon film 807 added withboron at a concentration of 1×10¹⁵ to 1×10¹⁸ atoms/cm³ is obtained.Boron added here is an impurity element for adjusting the thresholdvoltage of the transistor.

[0142] Further, by providing the protecting film 805, a fine adjustmentof concentration may be performed. Note that, in this embodiment, anexample of adding boron to the entire crystalline silicon film 806 isshown, but boron may be added partially by using a mask. Further, ann-type impurity element may be added, or an n-type impurity element anda p-type impurity element may be added.

[0143] Next, a protecting film 805 is removed and laser annealing isperformed for the exposed crystalline silicon film 807. As a laser, asolid-state laser (typically, an Nd:YAG laser) or an excimer laser maybe used. By this laser annealing, a crystalline silicon film 808 withimproved crystallinity may be obtained.

[0144] Note that, the order of the crystallization process by furnaceannealing, the doping process of a p-type impurity element and the laserannealing process may be switched. For example, the doping process ofthe p-type impurity element may be conducted before the crystallizationprocess by furnace annealing, or after a laser annealing process.

[0145] After a crystalline silicon film 808 is obtained as describedabove, an active matrix type light emitting device is manufacturedaccording to the processes after FIG. 2B of Embodiment 1. However, whenimplementing this embodiment, metal elements such as nickel, palladium,cobalt, platinum, copper, and iridium are contained in the crystallinesilicon film which is to be an active layer. Such a metal element maybecome a silicide and may become a path of current that leaks, so it ispreferably removed as much as possible.

[0146] Then, in this embodiment nickel in the crystalline silicon filmis reduced by gettering nickel with phosphorus. For that reason, thetemperature of the activation process shown in FIG. 3C is set quite highat 500 to 600° C. FIG. 9 shows the above description.

[0147] When the activation process is performed in the temperature rangeof 500 to 600° C., simultaneously nickel moves in the direction of thearrow in FIG. 9, to thereby be captured (gettered) in the region dopedwith phosphorus. Therefore, the concentration of nickel in the regionshown by reference numerals 901 to 905 (the channel forming region oftransistors) is reduced to 1×10¹⁷ atoms/cm³ or less in measurement ofSIMS (secondary ion mass spectrometer).

[0148] The transistor manufactured according to the structure of thisembodiment has good crystallinity of the active layer (especially thechannel forming region), and shows high electric field effect mobility,and small subthreshold coefficient. Therefore a transistor with fastoperating speed may be formed.

[0149] Note that, the structure of this embodiment may be implemented incombination with any of the structures of Embodiments 1 to 3.

[0150] (Embodiment 5)

[0151] In this embodiment, a case of manufacturing an active matrix typelight emitting device with a manufacturing method different to that ofEmbodiment 1 is described.

[0152] In Embodiment 1, the process of forming the first inorganicinsulating film 256, the process of activation, the process of formingthe second inorganic insulating film 257, and the process of heattreatment at 350 to 450° C. are performed in this order, but the ordermay be switched.

[0153] First, the process of forming the first inorganic insulating film256, the process of forming the second inorganic insulating film 257,the process of activation, and the process of heat treatment at 350 to450° C. may be performed in that order.

[0154] Further, the process of forming the first inorganic insulatingfilm 256 may be omitted, so that the process of forming the secondinorganic insulating film 257, the process of activation, and theprocess of heat treatment at 350 to 450° C. may be performed in thatorder.

[0155] Further, the process of forming the first inorganic insulatingfilm 256 may be omitted, so that the process of activation, the processof forming the second inorganic insulating film 257, and the process ofheat treatment at 350 to 450° C. may be performed in that order.

[0156] Note that, the structure of this embodiment may be implemented incombination with any of the structures of Embodiments 1 to 4.

[0157] (Embodiment 6)

[0158] In this embodiment, an example of combining the use of an organiccompound which emits light by a singlet exciton (singlet) (hereinafter,referred to as a singlet compound), and an organic compound which emitslight by a triplet exciton (triplet) (hereinafter, referred to as atriplet compound) as a light emitting layer is described. Note that, asinglet compound refers to a compound which emits light through only asinglet excitation, and a triplet compound refers to a compound whichemits light through a triplet excitation.

[0159] As a triplet compound, the organic compounds disclosed in thearticles below may be given as typical materials.

[0160] (1) T. Tsutsui, C. Adachi, S. Saito, Photochemical Processes inOrganized Molecular Systems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo,1991) p. 437.

[0161] (2) M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley,M. E. Thompson, S. R. Forrest, Nature 395 (1998) p. 151.

[0162] In these articles there are disclosed organic compounds shown bythe following formulas.

[0163] (3) M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S.R. Forrest, Appl. Phys. Lett., 75 (1999) p.4.

[0164] (4) T. Tsutsui, M. J. Yang, M. Yahiro, K. Nakamura, T. Watanabe,T. Tsuji, Y. Fukuda, T. Wakimoto, S. Mayaguchi, Jpn. Appl. Phys., 38(12B) (1999) L1502.

[0165] Further, the present inventors consider that not only the lightemitting materials disclosed in the above articles, but also the lightemitting materials shown by the following molecular formulas(specifically, a metal complex or an organic compound) may be used.

[0166] Chemical Formula 1

[0167] Chemical Formula 2

[0168] In the above molecular formulas, M is an element belonging togroups 8 to 10 of the periodic table. In the above articles, platinumand iridium are used. Further, the present inventors consider that sincenickel, cobalt or palladium is cheaper than platinum or iridium, theyare more preferable in reducing the manufacturing cost of the lightemitting device. Especially, since nickel can easily form a complex,productivity is high and therefore preferable.

[0169] The above-mentioned triplet compound has higher luminousefficiency than the singlet compound, and in obtaining the same lightemitting brightness, the operation voltage (a voltage necessary for anEL element to emit light) may be decreased. This embodiment makes use ofthis feature.

[0170]FIG. 10 shows a cross sectional structure of the pixel portion ofthe active matrix type light emitting device of this embodiment. In FIG.10, reference numeral 10 shows an insulator, reference numeral 11 showsa current control transistor 604 of FIG. 4B, reference numeral 12 showsa pixel electrode (anode), reference numeral 13 shows a bank, referencenumeral 14 shows a known hole injecting layer, reference numeral 15shows a light emitting layer which emits red color, reference numeral 16shows a light emitting layer which emits green color, reference numeral17 shows a light emitting layer which emits blue color, referencenumeral 18 shows a known electron transporting layer, and referencenumeral 19 shows a cathode.

[0171] Here in this embodiment, a triplet compound is used as a lightemitting layer 15 which emits red color, and a singlet compound is usedas a light emitting layer 16 which emits green color and a lightemitting layer 17 which emits blue color. That is, an EL element using asinglet compound is an EL element which emits green color or blue color,and an EL element using the above-mentioned triplet compound is an ELelement which emits red color.

[0172] When a low molecular organic compound is used as a light emittinglayer, at present the life of a light emitting layer which emits redcolor is shorter than a light emitting layer which emits other coloredlight. This is because the luminous efficiency is lower than that ofother colors, and in order to obtain the same light emitting brightnessas other colors, the operation voltage has to be set higher and thusprogress of deterioration is fast.

[0173] However, in this embodiment since a triplet compound with highluminous efficiency is used as the light emitting layer 15 which emitsred color, the same light emitting brightness as the light emittinglayer 16 which emits green color and the light emitting layer 17 whichemits blue color may be obtained while the operation voltage is made thesame. Accordingly, the deterioration of the light emitting layer 15which emits red color does not progress significantly, and color displaymay be performed without causing a problem such as color shift. Further,suppression of the operation voltage is preferable considering that themargin of the peak inverse voltage of the transistor may be set low.

[0174] Note that, in this embodiment an example of using a tripletcompound as the light emitting layer 15 which emits red color is shown,and a triplet compound may be used as the light emitting layer 16 whichemits green color or the light emitting layer 17 which emits blue color.

[0175] A circuit structure of the pixel portion in the case thisembodiment is implemented is shown in FIG. 11. Note that, here the pixel(pixel (red)) 20 a which includes an EL element which emits red color,the pixel (pixel (green)) 20 b which includes an EL element which emitsgreen color, and the pixel (pixel (blue)) 20 c which includes an ELelement which emits blue color are shown, and all have the same circuitstructure.

[0176] In FIG. 11A, reference numeral 21 denotes a gate wiring line,reference numerals 22 a to 22 c denote source wiring lines (data wiringlines), and reference numerals 23 a to 23 c denote current supply wiringlines. The current supply wiring lines 23 a to 23 c are wiring lines fordetermining the operation voltage of the EL element, and the samevoltage is applied to any of the pixel 20 a which emits red color, thepixel 20 b which emits green color and the pixel 20 c which emits bluecolor. Therefore, the line width (thickness) of the wiring lines may allhave the same design.

[0177] Further, reference numerals 24 a to 24 c denote switchingtransistors, and here are formed of n-channel transistors. Note that, astructure having two channel forming regions in between the sourceregion and the drain region is illustrated here, but a structure withtwo or more, or one channel forming region may be used.

[0178] Further, symbols 25 a to 25 c are current control transistors,and a gate is connected to any of the switching transistors 24 a to 24c, a source is connected to any of the current supplying lines 23 a to23 c, and a drain is connected to any of EL elements 26 a to 26 c. Notethat, symbols 27 a to 27 c are capacitors, which hold a voltage to beapplied to the gate of the respective current supply lines 25 a to 25 c.However, the capacitors 27 a to 27 c may be omitted.

[0179] Note that, FIG. 11A shows an example where switching transistors24 a to 24 c formed of n-channel transistors and current controltransistors 25 a to 25 c formed of p-channel transistors are provided.However, as shown in FIG. 11B, switching transistors 28 a to 28 c formedof p-channel transistors and current control transistors 29 a to 29 cformed of n-channel transistors may be provided in the pixel (red) 30 a,the pixel (green) 30 b and the pixel (blue) 30 c, respectively.

[0180] Further, in FIGS. 11A and 11B, an example of providing twotransistors in one pixel is shown, but the number of transistors may betwo or more (typically 3 to 6). In such a case, the n-channel transistorand the p-channel transistor may be provided by combining them in anyway.

[0181] In this embodiment, an EL element 26 a is an EL element whichemits red color, and uses a triplet compound as the light emittinglayer. Further, an EL element 26 b is an EL element which emits greencolor, and an EL element 26 c is an EL element which emits blue color,and both use a singlet compound as the light emitting layer.

[0182] In this way, by using the triplet compound and the singletcompound properly, the operation voltage of the EL elements 26 a to 26 cmay all be made the same (10V or less, preferably 3 to 10 V).Accordingly, since the power source necessary for a light emittingdevice may be made the same at for example 3V or 5V, there is anadvantage that the circuit design may be easily made.

[0183] Note that, the structures of this embodiment may be implementedin combination with any of the structures of Embodiments 1 to 5.

[0184] (Embodiment 7)

[0185] In this embodiment, a case where the pixel portion and the drivercircuit are all formed by the n-channel transistor is described. Notethat, the manufacturing process of the n-channel transistor is inaccordance with Embodiment 1, therefore a description thereof isomitted.

[0186] A cross sectional structure of the light emitting device of thisembodiment is shown in FIG. 12. Note that, the basic structures are thesame as the cross sectional structure shown in FIG. 4B of Embodiment 1,so only the differences are described here.

[0187] In this embodiment, an n-channel transistors 1201 is provided inplace of a p-channel transistor 602, and a current control transistor1202 formed of an n-channel transistor is provided in place of a currentcontrol transistor 604.

[0188] Further, a wiring line 266 connected to the drain of the currentcontrol transistor 1202 functions as a cathode of an EL element, and anEL layer 1203, an anode 1204 formed of an oxide conductive film, and apassivation film 1205 are formed thereon. At this time, it is preferablethat the wiring line 266 is formed of a metal film containing an elementbelonging to group 1 or 2 of the periodic table, or at least the surfacecontacting the EL layer 1203 is formed of a metal film containing anelement belonging to group 1 or 2 of the periodic table.

[0189] Further, the n-channel transistor used in this embodiment may beall enhancement type transistors, or may be depression type transistors.Of course, it is possible to make both and combine them for use.

[0190] Here, the circuit structure of a pixel is shown in FIG. 13. Notethat, for the portion where the same symbols as FIG. 11 is used, thedescription of FIG. 11 may be referred to.

[0191] As shown in FIG. 13, the switching transistors 24 a to 24 cprovided in the pixel (red) 35 a, the pixel (green) 35 b, and the pixel(blue) 35 c, respectively, and the current control transistors 35 a to35 c are all formed of n-channel transistors.

[0192] According to the structure of this embodiment, in themanufacturing process of the light emitting device of Embodiment 1,since the photolithography process for forming a p-channel transistorand the photolithography process for forming a pixel electrode (anode)may be omitted, it is possible to further simplify the manufacturingprocess.

[0193] Note that, the structure of this embodiment may be implemented bycombining any of the structures of Embodiments 1 to 6.

[0194] (Embodiment 8)

[0195] In this embodiment, a case where the pixel portion and thedriving circuit are all formed by a p-channel transistor is described. Across sectional structure of a light emitting device of this embodimentis shown in FIG. 14. Note that, a portion with the same symbol as inFIG. 4B of Embodiment 1may refer to the description of Embodiment 1.

[0196] In this embodiment, the driving circuit is formed of a PMOScircuit formed of a p-channel transistor 1401 and a p-channel transistor1402, and the pixel portion has a switching transistor 1403 formed of ap-channel transistor and a current control transistor 1404 formed of ap-channel transistor. Note that, the active layer of the p-channeltransistor 1401 includes the source region 41, the drain region 42, theLDD regions 43 a and 43 b and the channel forming region 44. Thestructure of the active layer is the same as in the p-channel transistor1402, the switching transistor 1403 and the current control transistor1404.

[0197] Here, the manufacturing process of the p-channel transistor ofthis embodiment is described by referring to FIG. 15. First, the processuntil FIG. 2B is described in accordance with the manufacturing processof Embodiment 1.

[0198] Next, electrodes 212 to 216 which are formed of a secondconductive film are formed using resists 211 a to 211 e. Then, theresists 211 a to 211 e and the electrodes 212 to 216 formed of thesecond conductive film are used as masks and elements belonging to group13 of the periodic table (in this embodiment, boron) are added to asemiconductor film, thereby forming regions (hereinafter, referred to asp-type impurity region (a)) 301 to 309 containing boron at aconcentration of 1×10²⁰ to 1×10²¹ atoms/cm³ (FIG. 15A).

[0199] Next, the electrodes 212 to 216 formed of the second conductivefilm are etched using the resists 211 a to 211 e under the same etchingconditions as in FIG. 1D, to thereby form the second gate electrodes 310to 314 (FIG. 15B).

[0200] Next, the first conductive film 209 is etched under the sameetching conditions as in FIG. 1C, with the resists 211 a to 211 e andthe second gate electrodes 310 to 314 as masks, to thereby form firstgate electrodes 315 to 319.

[0201] Then, the element belonging to group 13 of the periodic table (inthis embodiment, boron) is doped into the semiconductor film, with theresists 211 a to 211 e and the second gate electrodes 310 to 314 asmasks, to thereby form regions (hereinafter, referred to as a p-typeimpurity region (b)) 320 to 329 containing boron at a concentration of1×10¹⁶ to 1×10¹⁹ atoms/cm³ (typically, 1×10¹⁷ to 1×10¹⁸ atoms/cm³) (FIG.15C).

[0202] The processes thereafter are in accordance with the processesafter FIG. 3C of Embodiment 1. With the above processes, the lightemitting device of the structure shown in FIG. 14 can be formed.

[0203] Note that, the p-channel transistors used in this embodiment mayall be enhancement type transistors, or may all be depletion typetransistors. Of course, both may be formed and combined to be used.

[0204] The circuit structure of the pixel is shown in FIG. 16. Notethat, the portion with the same symbols as in FIG. 11 may refer to thedescription of FIG. 11.

[0205] As shown in FIG. 16, the switching transistors 51 a to 51 c andthe current control transistors 52 a to 52 c provided respectively in apixel (red) 50 a, a pixel (green) 50 b, and a pixel (blue) 50 c are allformed of p-channel transistors.

[0206] According to the structure of this embodiment, since the firstphotolithography process in the manufacturing process of the lightemitting device of Embodiment 1 may be omitted, the manufacturingprocess may be simplified more than in Embodiment 1.

[0207] Note that, the structure of this embodiment may be implemented incombination with any of the structures of Embodiments 1 to 6.

[0208] (Embodiment 9)

[0209] The active matrix type light emitting device of this inventionmay use, as a semiconductor element, a MOS (Metal Oxide Semiconductor)transistor. In such a case, a MOS transistor formed with a known methodmay be used as the semiconductor substrate (typically, a silicon wafer).

[0210] Note that, the structure of this embodiment may be implemented incombination with the structures of Embodiments 1 to 3, and 5 to 8.

[0211] (Embodiment 10)

[0212] In Embodiment 1, a driving circuit built-in light emitting deviceshown in FIG. 5 is an example of a pixel portion and a driving circuitintegrally formed on the same insulator, but a driving circuit may alsobe provided with an externally mounted IC (integrated circuit). In sucha case, the structure is as shown in FIG. 17A.

[0213] In the module shown in FIG. 17A, an FPC 63 is mounted on anactive matrix substrate 60 (including a pixel portion 61, wiring 62 aand 62 b), and a printed wiring board 64 is mounted through the FPC 63.Here, the functional block diagram of the printed wiring board 64 isshown in FIG. 17B.

[0214] As shown in FIG. 17B, the printed wiring board 64 is providedwith at least I/O ports (also referred to as an input or output portion)65 and 68, and an IC which functions as a source side driver circuit 66and a gate side driver circuit 67.

[0215] In this way, a module with a structure where an active matrixsubstrate formed with a pixel portion on the substrate surface ismounted with an FPC, and a structure where a printed wiring board havinga function as a driving circuit through the FPC is referred to as alight emitting module having an external driving circuit particularlythroughout this specification.

[0216] Further, in the module shown in FIG. 18A, a driving circuitbuilt-in light emitting device 70 (including a pixel portion 71, asource side driving circuit 72, a gate side driving circuit 73, wiringlines 72 a and 73 a) is mounted with an FPC 74, and a printed wiringboard 75 is mounted through the FPC 74. The functional block diagram ofa printed wiring board 75 is shown in FIG. 18B.

[0217] As shown in FIG. 18B, the printed wiring board 75 is providedwith at least an I/O port 76 and 79, and an IC which functions as acontrol portion 77. Note that here a memory portion 78 is provided, butit is not always necessary. Further, the control portion 77 is a portionhaving a function for controlling the driving circuit, correctingpicture data, and the like.

[0218] A module with a structure where a driving circuit built-in lightemitting device formed with a pixel portion and a driving circuit on theboard surface is mounted with a printed wiring board having a functionas a controller in this way, is referred to as a light emitting modulewith an external controller particularly in this specification.

[0219] (Embodiment 11)

[0220] The light-emitting device (including the module at the state ofwhich is shown in Embodiment 10) formed by implementing this inventionmay be used as a display portion of various electrical appliances. Aselectrical appliances of this invention, there are such as an imageplayback device with a video camera, a digital camera, a goggle typedisplay (head mounted display), a car navigation system, an audioapparatus, a note type personal computer, a game apparatus, a portableinformation terminal (such as a mobile computer, a portable telephone, aportable game apparatus or an electronic book), and an imagereprodiction device providing a recording medium. Specific examples ofthe electronic equipment are shown in FIGS. 19 and 20.

[0221]FIG. 19A shows an EL display and includes a casing 2001, asupporting base 2002 and a display portion 2003. The light-emittingdevice of this invention may be used for the display portion 2003. Whenusing the light-emitting device having the EL element in the displayportion 2003, since the EL element is a self-light emitting typebacklight is not necessary and the display portion may be made thin.

[0222]FIG. 19B shows a video camera, which contains a main body 2101, adisplay portion 2102, a sound input portion 2103, operation switches2104, a battery 2105, and an image receiving portion 2106. Thelight-emitting device of this invention can be applied to the displayportion 2102.

[0223]FIG. 19C shows a digital camera, which contains a main body 2201,a display portion 2202, an eye contact portion 2203, and operationswitches 2204. The light emitting-device and the liquid crystal displaydevice of this invention can be applied to the display portion 2202.

[0224]FIG. 19D shows an image playback device equipped with a recordingmedium (specifically, a DVD playback device), which contains a main body2301, a recording medium (such as a CD, LD or DVD) 2302, operationswitches 2303, a display portion (a) 2304, a display portion (b) 2305and the like. The display portion (a) is mainly used for displayingimage information. The display portion (b) 2305 is mainly used fordisplaying character information. The light-emitting device of thisinvention can be applied to the display portion (a) and the displayportion (b). Note that, the image playback device equipped with therecording medium includes devices such as CD playback device, and gamemachines.

[0225]FIG. 19E shows a portable (mobile) computer, which contains a mainbody 2401, a display portion 2402, an image receiving portion 2403,operation switches 2404 and a memory slot 2405. The light-emittingdevice of this invention can be applied to the display portion 2402.This portable computer may record information to a recording medium thathas accumulated flash memory or involatile memory, and playback suchinformation.

[0226]FIG. 19F shows a personal computer, which contains a main body2501, a casing 2502, a display portion 2503, and a keyboard 2504. Thelight-emitting device of this invention can be applied to the displayportion 2503.

[0227] The above electronic appliances more often display informationsent through electron communication circuits such as the internet or theCATV (cable television), and especially image information display isincreasing. When using the light-emitting device having the EL elementin the display portion, since the response speed of the EL element isextremely fast, it becomes possible to display pictures without delay.

[0228] Further, since the light emitting portion of the light-emittingdevice consumes power, it is preferable to display information so thatthe light emitting portion is as small as possible. Therefore, whenusing the light-emitting device in the portable information terminal,especially in the display portion where character information is mainlyshown in a portable phone or an audio apparatus, it is preferable todrive so that the character information is formed of a light emittingportion with the non-light emitting portion as a background.

[0229] Here, FIG. 20A shows a portable telephone, and reference numeral2601 shows a portion (operation portion) which performs key operation,and reference numeral 2602 shows a portion which performs informationdisplay (information display portion), and the operation portion 2601and the information display portion 2602 are connected by the connectingportion 2603. Further, the operation portion 2601 is provided with asound input portion 2604, operation switches 2605, and the informationdisplay potion 2602 is provided with a sound output portion 2606, adisplay portion 2607.

[0230] The light-emitting device of this invention may be used as thedisplay portion 2607. Note that, when using the light-emitting device tothe display portion 2607, the consumption power of the portabletelephone may be suppressed by displaying white letters in thebackground of the black color.

[0231] In the case of the portable telephone shown in FIG. 20A, thelight-emitting device used in the display portion 2604 is incorporatedwith a sensor by a CMOS circuit(a CMOS sensor), and may be used as anauthentication system terminal for authenticating the user by readingthe fingerprints or the hand of the user. Further, light emission may beperformed by taking into consideration the brightness (illumination) ofoutside and making information display at a contrast that is alreadyset.

[0232] Further, the low power consumption may be attained by decreasingthe brightness when using the operating switch 2605 and increasing thebrightness when the use of the operation switch is finished. Further,the brightness of the display portion 2604 is increased when a call isreceived, and low power consumption is attained by decreasing thebrightness during a telephone conversation. Further, when using thetelephone continuously, by making it have a function so that display isturned off by time control unless it is reset, low power consumption isrealized. It should be noted that this control may be operated by hand.

[0233] Further, FIG. 20B shows an audio, which contains a casing 2701, adisplay portion 2702, and operation switches 2703 and 2704. Thelight-emitting device of this invention can be applied to the displayportion 2702. Further, in this embodiment, a car mounted audio (caraudio) is shown, but it may be used in a fixed type audio (audiocomponent). Note that, when using a light-emitting device in the displayportion 2704, by displaying white characters in a black background,power consumption may be suppressed.

[0234] Further, electrical equipments shown above are incorporated witha light sensor in the light-emitting device which are used in thedisplay portion, and it is possible to provide means to detect thebrightness of the environment of use. When using the light-emittingdevice in the display portion, it is may have a function that modulatesthe light-emission brightness according to the brightness of theenvironment of use.

[0235] Specifically, this is implemented by providing an image sensor(surface shape, linear or a dotted sensor) formed by a CMOS circuit onthe light-emitting device using the display portion, and providing a CCD(charge coupled device) on the main body or the casing. The user mayrecognize the image or the character information without trouble if abrightness of a contrast ratio of 100 to 150 may be maintained ascompared to the brightness of the environment of use. Namely, in thecase the environment of use is dark, it is possible to suppress theconsumption power by suppressing the brightness of the image.

[0236] As in the above, the applicable range of this invention isextremely wide, and may be used for various electrical equipment.Further, the electrical equipment of this embodiment may use thelight-emitting device and the module containing any of the structures ofEmbodiments 1 to 10.

[0237] By carrying out the present invention, a light emitting devicecan be manufactured at a high yield and a low cost, and an inexpensivelight emitting device can be provided. Besides, it becomes possible toprovide an inexpensive electric instrument by using the inexpensivelight emitting device as a display portion.

What is claimed is:
 1. A method of fabricating a light emitting device,comprising the steps of: forming a semiconductor film on an insulator;forming a gate insulating film covering the semiconductor film; forminga first conductive film and a second conductive film on the gateinsulating film; forming an electrode made of the second conductive filmby etching the second conductive film; adding an n-type impurity elementto the semiconductor film by self-alignment using the electrode made ofthe second conductive film; forming an electrode made of the firstconductive film by etching the first conductive film by self-alignmentusing the electrode made of the second conductive film; forming a secondgate electrode by narrowing a line width of the electrode made of thesecond conductive film by etching; adding an n-type impurity element tothe semiconductor film by self-alignment using the second gateelectrode; and forming a first gate electrode by narrowing a line widthof the electrode made of the first conductive film by etching.
 2. Amethod of fabricating a light emitting device, comprising the steps of:forming a semiconductor film on an insulator; forming a gate insulatingfilm covering the semiconductor film; forming a first conductive filmand a second conductive film on the gate insulating film; forming anelectrode made of the second conductive film by etching the secondconductive film; adding an n-type impurity element to the semiconductorfilm by using the electrode made of the second conductive film as a maskand by making the n-type impurity element pass through the firstconductive film; forming an electrode made of the first conductive filmby etching the first conductive film by self-alignment using theelectrode made of the second conductive film; forming a second gateelectrode by narrowing a line width of the electrode made of the secondconductive film by etching; adding an n-type impurity element to thesemiconductor film by using the second gate electrode as a mask and bymaking the n-type impurity element pass through the electrode made ofthe first conductive film; and forming a first gate electrode bynarrowing a line width of the electrode made of the first conductivefilm by etching.
 3. A method of fabricating an electrical appliancehaving a light emitting device, comprising the steps of: forming asemiconductor film on an insulator; forming a gate insulating filmcovering the semiconductor film; forming a first conductive film and asecond conductive film on the gate insulating film; forming an electrodemade of the second conductive film by etching the second conductivefilm; adding an n-type impurity element to the semiconductor film byself-alignment using the electrode made of the second conductive film;forming an electrode made of the first conductive film by etching thefirst conductive film by self-alignment using the electrode made of thesecond conductive film; forming a second gate electrode by narrowing aline width of the electrode made of the second conductive film byetching; adding an n-type impurity element to the semiconductor film byself-alignment using the second gate electrode; and forming a first gateelectrode by narrowing a line width of the electrode made of the firstconductive film by etching.
 4. A method of fabricating an electricalappliance having a light emitting device, comprising the steps of:forming a semiconductor film on an insulator; forming a gate insulatingfilm covering the semiconductor film; forming a first conductive filmand a second conductive film on the gate insulating film; forming anelectrode made of the second conductive film by etching the secondconductive film; adding an n-type impurity element to the semiconductorfilm by using the electrode made of the second conductive film as a maskand by making the n-type impurity element pass through the firstconductive film; forming an electrode made of the first conductive filmby etching the first conductive film by self-alignment using theelectrode made of the second conductive film; forming a second gateelectrode by narrowing a line width of the electrode made of the secondconductive film by etching; adding an n-type impurity element to thesemiconductor film by using the second gate electrode as a mask and bymaking the n-type impurity element pass through the electrode made ofthe first conductive film; and forming a first gate electrode bynarrowing a line width of the electrode made of the first conductivefilm by etching.
 5. A method of fabricating a light emitting devicehaving at least one thin film transistor in a pixel portion, comprisingthe steps of: forming a semiconductor film on an insulator; forming agate insulating film covering the semiconductor film; forming a firstconductive film and a second conductive film on the gate insulatingfilm; forming an electrode made of the second conductive film by etchingthe second conductive film; adding an n-type impurity element to thesemiconductor film by self-alignment using the electrode made of thesecond conductive film; forming an electrode made of the firstconductive film by etching the first conductive film by self-alignmentusing the electrode made of the second conductive film; forming a secondgate electrode by narrowing a line width of the electrode made of thesecond conductive film by etching; adding an n-type impurity element tothe semiconductor film by self-alignment using the second gateelectrode; and forming a first gate electrode by narrowing a line widthof the electrode made of the first conductive film by etching.
 6. Amethod of fabricating a light emitting device having a pixel portion anda driver circuit formed over a same substrate, comprising the steps of:forming a semiconductor film on an insulator; forming a gate insulatingfilm covering the semiconductor film; forming a first conductive filmand a second conductive film on the gate insulating film; forming anelectrode made of the second conductive film by etching the secondconductive film; adding an n-type impurity element to the semiconductorfilm by self-alignment using the electrode made of the second conductivefilm; forming an electrode made of the first conductive film by etchingthe first conductive film by self-alignment using the electrode made ofthe second conductive film; forming a second gate electrode by narrowinga line width of the electrode made of the second conductive film byetching; adding an n-type impurity element to the semiconductor film byself-alignment using the second gate electrode; and forming a first gateelectrode by narrowing a line width of the electrode made of the firstconductive film by etching.
 7. A method of fabricating a light emittingdevice according to claim 1 , wherein an n-type impurity region (a) isformed at the former adding step, and an n-type impurity region (b) isformed at the latter adding step.
 8. A method of fabricating a lightemitting device according to claim 2 , wherein an n-type impurity region(a) is formed at the former adding step, and an n-type impurity region(b) is formed at the latter adding step.
 9. A method of fabricating anelectrical appliance having a light emitting device according to claim 3, wherein an n-type impurity region (a) is formed at the former addingstep, and an n-type impurity region (b) is formed at the latter addingstep.
 10. A method of fabricating an electrical appliance having a lightemitting device according to claim 4 , wherein an n-type impurity region(a) is formed at the former adding step, and an n-type impurity region(b) is formed at the latter adding step.
 11. A method of fabricating alight emitting device according to claim 5 , wherein an n-type impurityregion (a) is formed at the former adding step, and an n-type impurityregion (b) is formed at the latter adding step.
 12. A method offabricating a light emitting device according to claim 6 , wherein ann-type impurity region (a) is formed at the former adding step, and ann-type impurity region (b) is formed at the latter adding step.
 13. Amethod of fabricating a light emitting device according to claim 7 ,wherein a part of the n-type impurity region (b) overlaps the first gateelectrode through the gate insulating film.
 14. A method of fabricatinga light emitting device according to claim 8 , wherein a part of then-type impurity region (b) overlaps the first gate electrode through thegate insulating film.
 15. A method of fabricating a light emittingdevice according to claim 9 , wherein a part of the n-type impurityregion (b) overlaps the first gate electrode through the gate insulatingfilm.
 16. A method of fabricating a light emitting device according toclaim 10 , wherein a part of the n-type impurity region (b) overlaps thefirst gate electrode through the gate insulating film.
 17. A method offabricating a light emitting device according to claim 11 , wherein apart of the n-type impurity region (b) overlaps the first gate electrodethrough the gate insulating film.
 18. A method of fabricating a lightemitting device according to claim 12 , wherein a part of the n-typeimpurity region (b) overlaps the first gate electrode through the gateinsulating film.
 19. A method of fabricating a light emitting deviceaccording to claim 1 , wherein the first conductive film is a tantalumnitride film, and the second conductive film is a tungsten film.
 20. Amethod of fabricating a light emitting device according to claim 2 ,wherein the first conductive film is a tantalum nitride film, and thesecond conductive film is a tungsten film.
 21. A method of fabricatingan electrical appliance having a light emitting device according toclaim 3 , wherein the first conductive film is a tantalum nitride film,and the second conductive film is a tungsten film.
 22. A method offabricating an electrical appliance having a light emitting deviceaccording to claim 4 , wherein the first conductive film is a tantalumnitride film, and the second conductive film is a tungsten film.
 23. Amethod of fabricating a light emitting device according to claim 5 ,wherein the first conductive film is a tantalum nitride film, and thesecond conductive film is a tungsten film.
 24. A method of fabricating alight emitting device according to claim 6 , wherein the firstconductive film is a tantalum nitride film, and the second conductivefilm is a tungsten film.
 25. A method of fabricating a light emittingdevice according to claim 1 , wherein the first conductive film is atungsten film, and the second conductive film is an aluminum alloy film.26. A method of fabricating a light emitting device according to claim 2, wherein the first conductive film is a tungsten film, and the secondconductive film is an aluminum alloy film.
 27. A method of fabricatingan electrical appliance having a light emitting device according toclaim 3 , wherein the first conductive film is a tungsten film, and thesecond conductive film is an aluminum alloy film.
 28. A method offabricating a n electrical appliance a light emitting device accordingto claim 4 , wherein the first conductive film is a tungsten film, andthe second conductive film is an aluminum alloy film.
 29. A method offabricating a light emitting device according to claim 5 , wherein thefirst conductive film is a tungsten film, and the second conductive filmis an aluminum alloy film.
 30. A method of fabricating a light emittingdevice according to claim 6 , wherein the first conductive film is atungsten film, and the second conductive film is an aluminum alloy film.31. A method of fabricating an electrical appliance having a lightemitting device according to claim 3 , wherein said electrical applianceis an appliance selected from the group consisting of: a video camera, adigital camera, a DVD, a portable computer, a personal computer, aportable telephone and an audio.
 32. A method of fabricating anelectrical appliance having a light emitting device according to claim 4, wherein said electrical appliance is an appliance selected from thegroup consisting of: a video camera, a digital camera, a DVD, a portablecomputer, a personal computer, a portable telephone and an audio.